In an advanced wireless fidelity (Wi-Fi) network such as a high-efficiency wireless local area network (WLAN), access to the wireless medium may be allocated using orthogonal frequency-division multiple access (OFDMA). The use of OFDMA may provide the flexibility of allocating medium access at a sub-channel level of granularity. A trigger frame (TF) may be defined for use by an access point (AP) in such a network to notify stations (STAs) of sub-channels that have been allocated to them during particular intervals. A TF that allows random access (TF-R) may be defined for use by an AP in such a network to notify STAs of intervals during which they may contend for use of sub-channels. An AP may transmit multiple TFs within a given beacon interval, and/or may schedule one or more TF-Rs during that beacon interval. According to some techniques, the AP may include a TF-R Start Time for a first scheduled TF-R in the beacon frame for that beacon interval.
In some wireless networks in which an AP uses TF and TF-R frames to provide STAs with medium access information, the AP may also define one or more Target Wake Time (TWT) Groups. After having defined a given TWT Group, the AP may include a TWT Start Time for that TWT Group in a beacon frame for a beacon interval. The TWT Start Time may identify a subsequent point in time during the beacon interval at which a TWT interval for the TWT Group is to begin. Following receipt of the beacon frame, the STAs in the TWT Group may enter a sleep state, in which they may remain until returning to an awake state during the TWT interval beginning at the TWT Start Time.